Semiconductor device and method for fabricating the same

ABSTRACT

A method for fabricating semiconductor device includes the steps of: providing a substrate having a first region and a second region; forming a first fin-shaped structure on the first region and a second fin-shaped structure on the second region; forming a shallow trench isolation (STI) around the first fin-shaped structure and the second fin-shaped structure; forming a mask layer on the first fin-shaped structure; and performing a first anneal process so that the first fin-shaped structure and the second fin-shaped structure comprise different radius of curvature.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 15/885,834filed Feb. 1, 2018, and incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for fabricating semiconductor device,and more particularly to a method of using anneal process to formfin-shaped structures with different radius of curvature.

2. Description of the Prior Art

With the trend in the industry being towards scaling down the size ofthe metal oxide semiconductor transistors (MOS), three-dimensional ornon-planar transistor technology, such as fin field effect transistortechnology (FinFET) has been developed to replace planar MOStransistors. Since the three-dimensional structure of a FinFET increasesthe overlapping area between the gate and the fin-shaped structure ofthe silicon substrate, the channel region can therefore be moreeffectively controlled. This way, the drain-induced barrier lowering(DIBL) effect and the short channel effect are reduced. The channelregion is also longer for an equivalent gate length, thus the currentbetween the source and the drain is increased. In addition, thethreshold voltage of the fin FET can be controlled by adjusting the workfunction of the gate.

However, the design of fin-shaped structure in current FinFETfabrication still resides numerous bottlenecks which induces currentleakage of the device and affects overall performance of the device.Hence, how to improve the current FinFET fabrication and structure hasbecome an important task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forfabricating semiconductor device includes the steps of: providing asubstrate having a first region and a second region; forming a firstfin-shaped structure on the first region and a second fin-shapedstructure on the second region; forming a shallow trench isolation (STI)around the first fin-shaped structure and the second fin-shapedstructure; forming a mask layer on the first fin-shaped structure; andperforming a first anneal process so that the first fin-shaped structureand the second fin-shaped structure comprise different radius ofcurvature.

According to another aspect of the present invention, a semiconductordevice includes: a substrate having a first region and a second regionand a first fin-shaped structure on the first region and a secondfin-shaped structure on the second region. Preferably, the firstfin-shaped structure and the second fin-shaped structure comprisedifferent radius of curvature.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-7 illustrate a method for fabricating semiconductor deviceaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-7, FIGS. 1-7 illustrate a method for fabricatingsemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 1, a substrate 12, such as a siliconsubstrate or silicon-on-insulator (SOI) substrate is first provided anda plurality of fin-shaped structures 14 are formed on the substrate 12.In this embodiment, a first region 16 and a second region 18 are definedon the substrate 12, in which the first region 16 and the second region18 are preferably used to fabricate devices having different electricfields in the later process. It should be noted that even though fourfin-shaped structures 14 are formed on each of the first region 16 andthe second region 18 in this embodiment, the number of the fin-shapedstructures could be adjusted according to the demand of the product.

According to an embodiment of the present invention, the fin-shapedstructures 14 could be obtained by a sidewall image transfer (SIT)process. For instance, a layout pattern is first input into a computersystem and is modified through suitable calculation. The modified layoutis then defined in a mask and further transferred to a layer ofsacrificial layer on a substrate through a photolithographic and anetching process. In this way, several sacrificial layers distributedwith a same spacing and of a same width are formed on a substrate. Eachof the sacrificial layers may be stripe-shaped. Subsequently, adeposition process and an etching process are carried out such thatspacers are formed on the sidewalls of the patterned sacrificial layers.In a next step, sacrificial layers can be removed completely byperforming an etching process. Through the etching process, the patterndefined by the spacers can be transferred into the substrate underneath,and through additional fin cut processes, desirable pattern structures,such as stripe patterned fin-shaped structures could be obtained.

Alternatively, the fin-shaped structures 14 could also be obtained byfirst forming a patterned mask (not shown) on the substrate, 12, andthrough an etching process, the pattern of the patterned mask istransferred to the substrate 12 to form the fin-shaped structure.Moreover, the formation of the fin-shaped structures 14 could also beaccomplished by first forming a patterned hard mask (not shown) on thesubstrate 12, and a semiconductor layer composed of silicon germanium isgrown from the substrate 12 through exposed patterned hard mask viaselective epitaxial growth process to form the corresponding fin-shapedstructure. These approaches for forming fin-shaped structure are allwithin the scope of the present invention.

Next, a shallow trench isolation (STI) is formed around the fin-shapedstructures 14. In this embodiment, the formation of the STI 14 could beaccomplished by first conducting a flowable chemical vapor deposition(FCVD) process to form an insulating layer 20 made of silicon oxide onthe substrate 12 and covering the fin-shaped structures 14 entirely.Next, a planarizing process including but not limited to for example achemical mechanical polishing (CMP) process is conducted to remove partof the insulating layer 20 so that the top surface of the remaininginsulating layer 20 is even with the top surface of the fin-shapedstructures 14.

Next, as shown in FIG. 2, an etching process is conducted to remove partof the insulating layer 20 so that the top surface of the remaininginsulating layer 20 is slightly lower than the top surface of thefin-shaped structures 14 on the first region 16 and second region 18.This forms the STI 22 around the fin-shaped structures 14.

Next, as shown in FIG. 3, a mask layer 24 is formed on the fin-shapedstructures 14 on the first region 16 and the second region 18, and aphoto-etching process or pattern transfer process is conducted to removepart of the mask layer 24 on the second region 18. For instance, itwould be desirable to first form a patterned mask (not shown) such aspatterned resist to cover the mask layer 24 on the first region 16 andthen conduct an etching process by using the patterned resist as mask toremove the mask layer 24 on the second region 18 not covered by thepatterned resist. This forms a patterned mask layer 24 on the firstregion 16 and at the same time exposes the fin-shaped structures 14 onthe second region 18, and the patterned resist is stripped thereafter.In this embodiment, the mask layer 24 preferably includes siliconnitride and the etching process conducted to remove part of the masklayer 24 could include etchant including but not limited to for examplephosphoric acid. It should be noted that none of the fin-shapedstructures 14 is damaged as part of the mask layer 24 on the secondregion 18 is removed during the aforementioned etching process so thatafter the mask layer 24 is removed, the top surface of each of thefin-shaped structures 14 on the second region 18 preferably includes aplanar surface.

Next, as shown in FIG. 4, a first anneal process 28 is conducted toinduce a silicon migration on the tip of each of the fin-shapedstructures 14 not covered by the mask layer 24 so that the profile ofthe top surface of the fin-shaped structures 14 not covered by the masklayer 24 is altered and at the same time the electric field andperformance of the fin-shaped structures 14 are also adjusted.Specifically, as the fin-shaped structures 14 on the first region 16 arecovered by the mask layer 24 before the anneal process is conducted, thetip or topmost surface of each of the fin-shaped structures 14 on thesecond region 18 is transformed into a first curved surface 26 duringthe first anneal process 28 while the fin-shaped structures 14 on thefirst region 16 remain unchanged. In other words, silicon migration wasoccurred only on the tip of the fin-shaped structures 14 on the secondregion 18 to transform the planar topmost surface of each of thefin-shaped structures 14 into a curved surface during the first annealprocess 28 as the tip of the fin-shaped structures 14 on the secondregion 18 are not covered or protected by the mask layer 24. No siliconmigration however was occurred on the tip of each of the fin-shapedstructures 14 on first region 16 so that the tip of each of thefin-shaped structures 14 on the first region 16 preferably remainsunchanged or planar after the first anneal process 28. In thisembodiment, the temperature of the first anneal process 28 is preferablybetween 700° C. to 850° C. and the pressure of the first anneal process28 is preferably between 5 Torr to 300 Torr, but not limited thereto.

Next, as shown in FIG. 5, an etching process is conducted preferablywithout forming extra patterned mask to remove the mask layer 24 on thefirst region 16 and expose the fin-shaped structures 14 underneath. Inthis embodiment, the etching process conducted to remove the mask layer24 could include etchant including but not limited to for examplephosphoric acid.

It should be noted the tip or topmost surface of each of the fin-shapedstructures 14 on the first region 16 and the second region 18 preferablyincludes a radius of curvature (R_(c)) at this stage, in which theradius of curvature in this embodiment is defined as distance measuredfrom any point from the tip or topmost surface of each fin-shapedstructure 14 to a center of curvature (C_(c)). As shown in the structurein FIG. 5, since the topmost surface of each of the fin-shapedstructures 14 on the first region 16 is a planar surface, the radius ofcurvature (R_(c)) of each fin-shaped structure 14 on the first region 16is infinite. The top surface of each of the fin-shaped structures 14 onsecond region 18 however is transformed from planar surface to firstcurved surface 26 during the aforementioned first anneal process 28,hence a first radius of curvature R₁ could be obtained by measuring thedistance from any point on the first curved surface 26 to a center ofcurvature (C_(e)) for each of the fin-shaped structures 14. At thisstage, as the radius of curvature of each fin-shaped structure 14 on thefirst region 16 is infinitely large, the first radius of curvature (R₁)of each fin-shaped structure 14 on the second region 18 is preferablyless than the radius of curvature of each fin-shaped structure 14 on thefirst region 16.

Next, as shown in FIG. 6, a selective second anneal process 30 could beconducted without forming any extra mask to transform the profile of thetip of each of the fin-shaped structures 14 once more and at the sametime adjust the electrical field of the fin-shaped structures 14.Specifically, since no mask layer 24 is disposed on the fin-shapedstructures 14 on the first region 16 at this stage, the second annealprocess 30 preferably alters the profile of the topmost surface offin-shaped structures 14 on both first region 16 and second region 18 atthe same time. Preferably, the planar top surface on each of thefin-shaped structures 14 on the first region 16 is transformed into asecond curved surface 32 and the first curved surface 26 on each of thefin-shaped structures 14 on second region 18 is transformed into a thirdcurved surface 34, in which each of the second curved surface 32 and thethird curved surface 34 being a completely curved surface withoutincluding any planar portion.

Viewing from a more detailed perspective regarding the change in theradius of curvature, since the planar topmost surface of each of thefin-shaped structures 14 on the first region 16 is transformed into asecond curved surface 32 through the aforementioned second annealprocess 30, a second radius of curvature R₂ could be obtained bymeasuring the distance from any point on the second curved surface 32 toa center of curvature (C_(c)). The topmost surface or first curvedsurface 26 with corresponding first radius of curvature R₁ of each ofthe fin-shaped structures 14 on the second region 18 on the other handis transformed into a third curved surface 34 with third radius ofcurvature R₃ after the second anneal process 30. Specifically, the thirdradius of curvature R₃ of the third curved surface 34 is slightly lessthan the second radius of curvature R₂ and the first radius of curvatureR₁ while the second radius of curvature R₂ and the first radius ofcurvature R₁ remain substantially the same. For instance, it would alsobe desirable to adjust the parameter of the fabrication process toobtain second radius of curvature R₂ that may be slightly less than orgreater than the first radius of curvature R₁, which are all within thescope of the present invention. It should also be noted that the firstradius of curvature R₁, second radius of curvature R₂, and the thirdradius of curvature R₃ shown in FIGS. 5-6 are not drawn to actual scalebut merely demonstrate a comparison between relative sizes of differentradius of curvatures. Similar to the aforementioned embodiment, thetemperature of the second anneal process 30 is preferably between 700°C. to 850° C. and the pressure of the second anneal process 30 ispreferably between 5 Torr to 300 Torr, but not limited thereto.

Next, as shown in FIG. 7, a transistor fabrication process could beconducted thereafter by sequentially forming a gate dielectric layer 36and a gate material layer 38 made of polysilicon on the fin-shapedstructures 14 on the first region 16 and second region 18, performing aphoto-etching process on the gate material layer 38 to form gatestructures, and then forming transistor elements such as spacers andsource/drain regions adjacent to two sides of the gate structure. Itshould be noted that even though the gate dielectric layer 36 and thegate material layer 38 are formed on the fin-shaped structures 14 afterthe second anneal process 30 is completed, it would also be desirable todirectly form the gate dielectric layer 36 and gate material layer 38 onthe fin-shaped structures 14 as soon as the mask layer 24 is removed inFIG. 5 and then conduct follow-up transistor fabrication processthereafter, which is also within the scope of the present invention.

Overall, the present invention first forms a plurality of fin-shapedstructures on a first region and second region of a substrate, form aSTI around the fin-shaped structures, and then form a mask layer tocover the fin-shaped structures on the first region. Next, an annealprocess is conducted by using high temperature to induce siliconmigration on the tip of the fin-shaped structures not covered by themask layer thereby altering the profile of the topmost surface of thefin-shaped structures so that the tip or topmost surfaces of thefin-shaped structures on the first region and second region would havedifferent radius of curvature. By doing so, the electric field andperformance of the fin-shaped structures on each of the first region andthe second region could be adjusted accordingly to produce fin-shapedstructures suitable for different products.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for fabricating semiconductor device,comprising: providing a substrate having a first region and a secondregion; forming a first fin-shaped structure on the first region and asecond fin-shaped structure on the second region; forming a shallowtrench isolation (STI) around the first fin-shaped structure and thesecond fin-shaped structure; forming a mask layer on the firstfin-shaped structure; and performing a first anneal process to transforma top surface of the second fin-shaped structure into a first curve sothat the first fin-shaped structure and the second fin-shaped structurecomprise different radius of curvature.
 2. The method of claim 1,further comprising: forming an insulating layer around the firstfin-shaped structure and the second fin-shaped structure; removing partof the insulating layer to form the STI.
 3. The method of claim 1,wherein the mask layer comprises silicon nitride.
 4. The method of claim1, wherein a top surface of each of the first fin-shaped structure andthe second fin-shaped structure comprises a planar surface.
 5. Themethod of claim 1, further comprising removing the mask layer afterperforming the first anneal process.
 6. The method of claim 5, furthercomprising performing a second anneal process after removing the masklayer to transform a top surface of the first fin-shaped structure intoa second curve and transform the first curve into a third curve.
 7. Themethod of claim 6, wherein a radius of curvature of the third curve isless than a radius curvature of the second curve.
 8. The method of claim1, wherein a difference between a height of the first fin-shapedstructure and a height of the second fin-shaped structure is less than10% of the height of the first fin-shaped structure.
 9. The method ofclaim 1, wherein a difference between a height of the first fin-shapedstructure and a height of the second fin-shaped structure is less than5% of the height of the first fin-shaped structure.